Multiply stacked electrochemical cell and method for preparing the same

ABSTRACT

The present invention relates to an electrochemical element, specifically an electrochemical element with improved energy density comprising stacked electrochemical cells. In order to achieve such objects, the present invention provides an electrochemical element comprising electrochemical cells which are multiply stacked, said electrochemical cells formed by stacking full cells or bicells having a cathode, a separator layer, and an anode sequentially as a basic unit, and a separator film interposed between each stacked cell wherein, said separator film has a unit length which is determined to wrap the electrochemical cells, and folds outward every unit length to fold each electrochemical cell in a Z-shape starting from the electrochemical cell of a first spot to the electrochemical cell of the last spot continuously while the remaining separator film wraps an outer portion of the stacked cell and a method for manufacturing the same.

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The present invention relates to an electrochemical element and amethod of manufacturing the same, specifically to an electrochemicalelement with improved energy density comprising multiply stackedelectrochemical cells and a method of manufacturing the same.

[0003] (b) Description of the Related Art

[0004] There has been growing interest on energy storage technology. Theapplicable field of the battery has been expanded to cellular phones,camcorders and notebook computers with recent addition of electricvehicles into this list. Such expansion has led to increased researchand development of batteries with visible outcomes. In this respect,researches on electrochemical elements are one of the fields that havebeen receiving much attention, among which rechargeable battery is thecentral field of interest. Recent developments have turned its way todesigning new batteries and electrodes to improve capacity and specificenergy.

[0005] Among the secondary batteries being used, lithium ion batterydeveloped in the 1990s has become increasingly popular because it hashigher operating voltage and energy density compared to Ni—MH, Ni—Cd,and sulfuric acid-lead batteries that use aqueous solution electrolyte.These lithium ion batteries, however, have safety problems resultingfrom the use of organic electrolyte, which causes the batteries to beflammable and explosive. Also, lithium ion has the weakness of havingdifficult manufacturing process. Recent lithium ion polymer batterieshave overcome such shortcomings of the lithium ion batteries and areanticipated to become the batteries of the next generation. Theselithium ion polymer batteries, however, have relatively low capacitycompared to lithium ion batteries and have especially insufficientdischarging capacity at low temperatures; and thus, need to be improved.

[0006] The capacity of the batteries is in proportion to the amount ofthe electrode active materials. Thus, it is extremely important todesign a cell structure that can be filled with as much quantities ofelectrode materials as possible within the limited space of the batterypackage. The most widely known and used type of cell structure is ajellyroll shaped structure used in a cylindrical or a prismatic battery.Such a structure is prepared by a process of coating and pressing activeelectrode material onto a metal foil which is used as a currentcollector, followed by cutting it into a shape of a strip havingpredetermined width and length, and then separating the anode andcathode using the separator film, and then winding it into a spiralform. Such a jellyroll structure is widely used for manufacturingcylindrical batteries. This structure, however, has small radius ofcurvature at the center portion of the spiral, which often results inextreme stresses at the bending surface of the electrode, often causingexfoliation of the electrode. This facilitates the deposition of lithiummetal at the center portion of the electrode during the repeated chargeand discharge of the battery, which may shorten the lifespan of thebattery while degrading the safety of the battery.

[0007] Generally, the widely known and used method of manufacturing athin prismatic shaped battery comprises aforesaid process of winding thespiral shaped jelly roll into an oval shape and then compressing it,followed by inserting it into a rectangular container. This method isnot free from aforesaid problems of reduced lifespan and safety, butrather has increased problems caused by the decrease in the radius ofcurvature due to the oval shape. Also, the problem of reducedperformance is greater because manufacturing a tight spiral structure isinherently impossible. Furthermore, discrepancy of the oval shape of thejelly role and the rectangular shape of the container reduces the rateof utilized volume. This is known to reduce approximately 20% of theweight energy density and 25% of the volume energy density when thecontainer is taken into account. In reality, a prismatic lithium ionbattery is reported to have lower capacity density and specific energycompared to a cylindrical one.

[0008] Recently, various patents and technologies proposing to solve theproblems of the spiral jelly roll type structure and providing cellstructures suitable for a prismatic container are being published. Theseproposals, however, only provides partial solution to the problems orcauses other problems more difficult to solve so that they have notbecome a practical solution. For example, U.S. Pat. No. 5,552,239describes a process of first placing and laminating a separator layer orpolymer electrolyte between the cathode and anode, then cutting it intoa form of a strip with predetermined length and width, followed bygradually folding a cell having an anode/separator layer/cathode layeredstructure into a square form. The inventors of the present inventionhave tried to replicate such a process but have found out that it wasdifficult to manufacture the cells for such a use. The laminated cellswere so stiff that it was difficult to fold and when it was folded byexerting force, the problem arose in the folded area because it wasfractured in a manner similar to the jellyroll typed cells.

[0009] In fan-folding method described in U.S. Pat. No. 5,300,373, thepressure and stresses at the inner layer of the abruptly bending portionare transferred to the outer layer and diverged so that twisting andstretching occur, finally resulting in a “dog bone” shaped cell. Thus,the problems of exfoliations, cracks, crumbles or snapping, encounteredin jelly role type structure also occur frequently. Also, the cells withthis structure are inherently prone to snapping; and therefore, thepossibility of making a practically applicable battery is very low.

[0010] Meanwhile, U.S. Pat. No. 5,498,489 attempted to solve and improvesuch problems in the bending portions. It provides a fundamental way ofavoiding exfoliation of the electrodes by leaving out the electrodes atthe folding portions and providing connections only through the use ofcurrent collectors and separator layers or polymer electrolyte portions.But, there is difficulty in composing such a cell. Furthermore, too muchcurrent collectors are used and the structure wastes too muchelectrolyte. Thus, the structure is not very practical because it hasmany inefficient factors.

SUMMARY OF THE INVENTION

[0011] It is an objective of the present invention to provide anelectrochemical element comprising electrochemical cells which aremultiply stacked, wherein it is easy to manufacture, and has a structuremaking efficient use of the space available and a method ofmanufacturing the same while considering the prior art.

[0012] It is another objective of the present invention to provide anelectrochemical element and a method of manufacturing the same that canmaximize the content of the active electrode material and can bemanufactured easily.

[0013] These and other objectives may be achieved by an electrochemicalelement comprising electrochemical cells which are multiply stacked,said electrochemical cells formed by stacking full cells having acathode, a separator layer, and an anode sequentially as a basic unit,and a separator film interposed between each stacked full cell wherein,

[0014] said separator film has a unit length which is determined to wrapthe electrochemical cells, and folds outward every unit length to foldeach electrochemical cell in a Z-shape starting from the electrochemicalcell of a first spot to the electrochemical cell of the last spotcontinuously while the remaining separator film wraps an outer portionof the stacked cell.

[0015] Also, the present invention provides a method of manufacturing anelectrochemical element using the full cell comprising the steps of,

[0016] a) placing a full cell on and below the separator filmcontinuously or alternately;

[0017] b) laminating said placed full cells and said separator film ofa); and

[0018] c) folding outward said laminated full cells and said separatorfilm of b) to the full cell adjacent next to the first full cell to foldeach full cell in a Z-shape and wrapping the remaining separator filmround an outer portion of the stacked full cell at least once so thateach full cell is stacked.

[0019] Furthermore, the present invention provides an electrochemicalelement comprising electrochemical cells which are multiply stacked,said electrochemical cells formed by stacking,

[0020] i) a bicell having a cathode; a separator layer; an anode;another separator layer; and another cathode sequentially as a basicunit; or

[0021] ii) a bicell having an anode; a separator layer; a cathode;another separator layer; and another anode sequentially as a basic unit;

[0022] and a separator film interposed between each stacked bicellswherein,

[0023] said separator film has a unit length which is determined to wrapthe electrochemical cells, and folds outward every unit length to foldeach electrochemical cell in a Z-shape starting from the electrochemicalcell of a first spot to the electrochemical cell of the last spotcontinuously while the remaining separator film wraps an outer portionof the stacked cell.

[0024] Still furthermore, the present invention provides a method ofmanufacturing an electrochemical element using the bicell comprising thesteps of

[0025] a) placing a bicell on and below the separator film continuouslyor alternately;

[0026] b) laminating said placed bicells and said separator film of a);and

[0027] c) folding outward said laminated bicells and said separator filmof b) to the bicell adjacent next to the first bicell to fold eachbicell in a Z-shape and wrapping the remaining separator film round anouter portion of the stacked bicell at least once so that each bicell isstacked.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 shows a layered structure of a full cell comprising aboth-side coated cathode, an anode and a separator layer.

[0029]FIG. 2 shows a layered structure of the cell where multiple fullcells are stacked and a separator film is interposed between stackedcells.

[0030]FIG. 3 shows a layered structure of a cell comprising multiplystacked full cells having a single side of an outermost electrode of anoutermost full cell coated and left as a foil, and having a separatorfilm interposed between the full cells.

[0031]FIG. 4a shows a layered structure of a bicell where a middle layeris an anode and both outer sides are cathodes.

[0032]FIG. 4b shows a layered structure of a bicell where a middle layeris a cathode and both outer sides are anodes.

[0033]FIG. 5 shows a layered structure of a cell where two types ofbicells are alternately stacked with an interposed separator filmbetween the bicells.

[0034]FIG. 6 shows a layered structure of a cell comprising bicellshaving a single side of an outermost electrode of an outermost bicellcoated and left as a foil and two types of bicells are alternatelystacked having a separator film interposed between the full cells.

[0035]FIG. 7 is a development figure of a battery where full cells aresequentially placed on a cut separator film and then laminated so thatthe full cells are accurately aligned for stacking.

[0036]FIG. 8 is a graph showing a charging and dischargingcharacteristic of the electrochemical element according to the presentinvention.

[0037]FIG. 9 is a development figure of a battery where full cells aresequentially placed on a cut separator film and then laminated so thatthe full cells are accurately aligned for stacking.

[0038]FIG. 10 is a development figure of a battery where bicells aresequentially placed on a cut separator film and then laminated so thatthe bicells are accurately aligned for stacking.

[0039]FIG. 11 shows a cycle characteristic of an electrochemical elementaccording to the present invention.

[0040]FIG. 12 is a development figure of a battery where bicells aresequentially placed on a cut separator film and then laminated so thatthe bicells are accurately aligned for stacking

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Hereinafter, the present invention will be discussed in detailwith reference to the figures.

[0042] [Function]

[0043] The present invention provides a cell structure and a method forthe preparation thereof which is more convenient to manufacture and usesspace more efficiently compared to conventional cells. The presentinvention provides a unique but a simple way of maximizing the contentof electrode active material in a prismatic battery while solvingvarious shortcomings of various conventional cell structures discussedabove. In principle, the present invention does not make avail oflongitudinally cut electrodes used for spiral winding or folding, butrather uses the method of stacking electrodes cut in a predeterminedform.

[0044] The electrochemical cells according to the present invention arestacked with a full cell or a bicell as a basic unit.

[0045] The full cell of the present invention has a structure where alayered construction of a cathode 7, an anode 8 and a separator layer 15is cut into a regular shape and regular size and then stacked as shownin FIG. 1. All the electrodes use current collectors 11 and 12 coatedwith electrode active material 13 and 14 on both sides. Such a structureis treated as a single unit cell to constitute a battery by stacking.For such a purpose, the electrodes and the separator films must be fixedto each other. For example, in a lithium rechargeable cell, the maincomponent of the cathodic material 14 is lithium intercalation materialssuch as lithium manganese oxide, lithium cobalt oxide, lithium nickeloxide or a complex oxide formed from a combination of aforesaid oxides,said cathodic material coated on the cathode current collector 12, thatis, a foil prepared from aluminum, nickel, or a combination thereof toform a cathode 8. Also the main component of the anodic material 13 islithium metal or lithium alloy, and lithium intercalation materials suchas carbon, petroleum coke, activated carbon, graphite or other carbons,said anode material 13 coated on anode current collector 11, that is, afoil prepared from copper, gold, nickel, copper alloy or a combinationthereof to form an anode 7.

[0046] The separator layer 15 includes a micro-porous polyethylene film,a micro-porous polypropylene film, or a multi-layer film prepared by acombination thereof, or a polymer film for solid polymer electrolyte orgel-type polymer electrolyte such as polyvinylidene fluoride,polyethylene oxide, polyacrylonitrile or polyvinylidene fluoridehexafluoropropylene copolymer. Furthermore, it is very efficient to usea polymer film for polymer electrolyte including a primary micro-porouspolymer layer and a secondary gelling polymer layer of polyvinylidenefluoride-chlorotrifluoroethylene copolymer described in Korean PatentApplication No. 99-57312. An important feature needed for the separatorlayer 15 is a bonding characteristic from laminating for constituting aunit cell which is a full cell.

[0047] The unit structure of the full cell 17 shown in FIG. 1 iscomposed of a cathode, a separator layer, and an anode sequentially. Theseparator layer 15 is naturally placed in the center of the cell. Aplurality of theses unit cells can be stacked in a number desired toimplement a battery with practical capacity. For example, FIG. 2 showsfive full cells sequentially stacked. The way of interposing a polymerseparator layer or a polymer separator film having micro porous forpolymer electrolyte is extremely important as explained above forseparator layer 15 and FIG. 2 shows a way the present inventionprovides.

[0048] The full cells 17 of the present invention are stacked by foldingthe longitudinally cut separator film 19 in a Z-shape starting from afull cell and then stacked one by one. Such a structure becomes a veryefficient structure because the outer active coating material not usedwithin a unit cell is shared with opposite electrode active coatingmaterial of another adjacent unit cell. The separator film 19 isfinished by fixing a tape 27 after finishing the folding and wrappingonce around the full cells. Furthermore, the finishing can usethermo-fusing besides taping. That is, the separator film itself isfixed and bonded by heat-sealing which carry out bring a thermo-weldingmachine, a hot plate, or etc into contact with the separator film. Thenumber of full cells to be stacked is determined according to thedesired capacity of the finished battery.

[0049] In the present invention, the structure 44 of FIG. 2 has anothermeaning. According to the experience of the inventors of the presentinvention, the surfaces between the separator films such as film forpolymer electrolyte film or the polymer separator layer and electrodesare important. When the battery is actually used after injecting liquidelectrolyte and packaging, it is subject to numerous charging anddischarging cycle. When the contact of the surface is not constantlymaintained and becomes unstable, the performance of the battery dropssuddenly and actual capacity of the battery decreases. According to thestructure of the battery, this effect can be shown from the beginning orcan be revealed as time passes by. Therefore, there is a need to exertpressure to constantly maintain the surfaces. The present inventionprovides a new cell structure and method of assembling as a way ofmaintaining the pressure while fundamentally solving above problem. Inthis context, FIG. 2 has another meaning.

[0050] As can be seen in structure 44 of FIG. 2, a way of stacking theunit cells of full cells while folding the separator film 19 in aZ-shape efficiently uses the electrodes between the full cells. Pressureformed by wrapping the full cells once around after the folding pressessurfaces between the polymer film of the polymer electrolyte or thepolymer separator layer and the electrodes formed by all the cells. Afinal finishing using a tape 27 is a measure to constantly maintain sucha pressure, which allows stable and constant contact between thesurfaces.

[0051] A different material or same material of polymer separator layeror polymer film for polymer electrolyte can be used for a separatorlayer 15 and separator film 19. The separator layer 15 must have bondingcharacteristic from laminating to constitute a unit cell which is a fullcell, but the separator film 19 does not need to have such acharacteristic because it is possible to fold the full cells 17 by theseparator film 19 for assembling. But, for another type of assemblingusing a cell structure as shown in structure 44 of FIG. 2, it ispreferable to use the separator film 19 that also has the bondingcharacteristic. In this respect, it may be most appropriate to use thepolymer film for polymer electrolyte as a separator film 19 comprising afirst micro-porous polymer layer and a second gelling polymer layer ofpolyvinylidene fluoride-chlorotrifluoroethylene copolymer for thebattery according to the present invention. When the new polymer film isused as the separator film 19, there can be a large variety ofassembling method in structure 44 of FIG. 2. That is, every full cell 17has two possible directions, that is the upper direction and the lowerdirection for bonding to the separator film 19. If there are five fullcells as in FIG. 2, there can be 2⁵ kinds of ways of assembling. In sucha method, after the separator film 19 is spread in a longitudinaldirection, full cells are disposed in upper or lower side of theseparator film 29 according to any of the 2⁵ ways, and then laminatedfollowed by simply folding in a Z-shape and wrapping once around. Themerit of this method is the facility of assembling process of designingand disposing.

[0052]FIG. 3 shows structure 45 which eliminates the unused outermostactive electrode material from the structure 44 of FIG. 2 so that thestructure has the maximum space efficiency. When another full cell 17′is defined as a full cell structure having one electrode coated on bothsides and the other electrode coated on a single side, structure 45 ofFIG. 3 adopts such a full cell 17′ so that the outermost activeelectrode material not used is left as a foil as shown in structure 44of FIG. 2. This results in the additional decrease in the thicknesswithout losing the capacity so that the spatce efficiency is increasedfurthermore. But, when the stacked cells are increased, it does not showmuch difference in space utilization efficiency compared to thestructure 44 of FIG. 2. Nevertheless, structure 45 of FIG. 3 iseffective in a very thin layer card typed battery recently beingdiscussed.

[0053] In the present invention, when a plurality of bicells is stackedas a unit cell, the space efficient cell structure is applied in amanner identical to the above method. For such a purpose, two types ofbicells 23 and 24 are respectively defined both of which uses aboth-side coated electrode as shown in FIGS. 4a and 4 b. The bicell 23has an anode placed in the middle and cathodes placed in both outersides whereas the bicell 24 has a cathode placed in the middle andanodes placed in both outer sides. The usable active electrode materialand polymer separator layer or polymer film for polymer electrolyte as aseparator layer 15 is same in detail as discussed above in the fullcells.

[0054] The structure 46 of FIG. 5 shows a way of constituting a batteryusing two types of bicells as basic unit cells. When the bicell 23 and24 are alternately stacked, and aforementioned polymer separator layeror separator film 19 such as polymer film for polymer electrolyte areinserted between the bicells in a Z-shape folding manner, the outeractive coating material not used within a bicell is naturally sharedwith an opposite polarity of another type of adjacent bicell, forming anew full cell which has a very efficient structure. As can be seen instructure 46 of FIG. 5, if the separator films 19 are interposedcontinuously between the cells and the bicells are alternately stacked,the polarity of the battery is naturally formed without discrepancy. Theoutermost stacked bicell of the battery can be either bicell 23 orbicell 24, the only difference being whether the unused electrodematerial is an anode or a cathode. The proportion of such unusedelectrodes decreases as the number of stacks increases and for electrodewith a practical thickness, only has little influence. In otherstructure 46, the way and structure of inserting the separator film 19is identical to those of full cell in every detail and the separatorfilm 19 and tape 27 functioning under such a structure also has the samemeaning.

[0055]FIG. 6 shows a structure 47 eliminating the outermost activeelectrode material from the structure 46 of FIG. 5 so that the structurehas a maximum space efficiency. When the primes(′) denote structureswhere only one out of two outer electrodes of the bicell is left as thefoil, a structure stacking a bicell 23′ as the outermost bicell of thebattery (it does not matter whether the outermost bicell is bicell 23′or bicell 24′) as in structure 47 of FIG. 6 leaves the unused portion ofthe outermost active electrode material as the foil so that thethickness is further reduced not losing the space efficiency. Thisallows the merit of directly being related to the space efficiency. Whenthe layers of bicells being stacked increase, it does not show muchdifference from structure 46 of FIG. 5 in terms of the space efficiency.In a thin layer card typed battery, however, the structure of stackedcell 47 of FIG. 6 is effective.

[0056] The battery structure provided in the present invention is veryeffective for a prismatic battery. Generally, liquid electrolyte isinjected when packaging. For such a purpose, aluminum prismatic can oran aluminum laminate film can be used as a container. The liquidelectrolyte is a salt of A⁺B⁻ dissolved or dissociated in an organicsolvent wherein the A⁺ comprises an alkaline metal cation such as Li⁺,Na⁺, or K⁺ or combination thereof, the B− comprises an anion PF₆ ⁻, BF₄⁻, Cl⁻, Br⁻, I⁻, ClO₄ ⁻, ASF₆ ⁻, CH₃CO₂ ⁻, CF₃SO₃ ⁻, N(CF₃SO₂)₂ ⁻ orC(CF₂SO₂)₃ ⁻ or combination thereof and the organic solvent comprisespropylene carbonate(PC), ethylene carbonate(EC), diethyl carbonate(DEC),dimethyl carbonate(DMC), dipropyl carbonate(DPC), dimethyl sulfoxide,acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofurane,N-methyl-2-pyrrolidone(NMP), ethylmethyl carbonate(EMC), orγ-butyrolactone or combination thereof. Unlike a jelly roll of a lithiumion battery, the constituents of the battery according to the presentinvention have a form coinciding with the form of the quadrilateralcontainer so that there will be no unused space within the container.Therefore, the energy density of the battery can be greatly increased toimplement a highly integrated battery having maximized spatialefficiency of active materials.

[0057] The electrochemical element of the present invention can beapplied to the various fields such as supercapacitors, ultracapacitors,primary batteries, secondary batteries, fuel cells, sensors,electrolysis devices, electrochemical reactors, and etc, besides lithiumsecondary batteries.

[0058] The present invention will be explained in detail with referenceto the examples. These examples, however, should not in any sense beinterpreted as limiting the scope of the present invention.

EXAMPLES Example 1

[0059] Preparing a Stacked Cell where a Full Cell is a Basic Unit

[0060] (Preparing a Cathode)

[0061] LiCoO₂:carbon black:PVDF, of which the weight ratio was95:2.5:2.5, was dispersed in NMP in order to prepare slurry, and thenthe slurry was coated on an aluminum foil. After sufficiently drying at130° C., the cathode was prepared by pressing.

[0062] A cathode of the full cell was prepared by coating the slurry onboth sides of aluminum foil. That is, the cathode has a cathodicmaterial coated on both sides of the aluminum cathode current collector.The thickness of the both-side coated cathode was 140 μm.

[0063] (Preparing an Anode)

[0064] Graphite:acetylene black:PVDF, of which the weight ratio was93:1:6, was dispersed in NMP in order to prepare slurry, and then theslurry was coated on a copper foil. After sufficiently drying at 130°C., the anode was prepared by pressing.

[0065] An anode of the full cell was prepared by coating the slurry onboth sides of copper foil. That is, the anode has an anodic materialcoated on both sides of the copper anode current collector. Thethickness of the both-side coated anode was 135 μm.

[0066] (Preparing a Separator Layer; a Separator Film; a Polymer Filmfor Polymer Electrolyte)

[0067] A multi-layer polymer film was prepared wherein polypropylenefilm having a microporous structure and a thickness of 16 μm was a firstpolymer separator layer and polyvinylidenefluoride-chlorotrifluoroethylene copolymer 32008(Solvay) was a secondgelling polymer. 6 g of the 32008 was added to 194 g of acetone andstirred at 50° C. After 1 hour, the completely dissolved transparent32008 solution was coated on the polypropylene first polymer separatorlayer by a dip coating process. The thickness of coated 32008 was 1 μmand the thickness of the final multi-layered polymer film was 18 μm.Here, a same material was used for the separator layer and the separatorfilm.

[0068] (Preparing a Full Cell)

[0069] Seven full cells 17 of FIG. 1 were prepared by cutting thecathode having cathodic material coated on both sides of a cathodecurrent collector to the size of 2.9 cm×4.3 cm of rectangle, except forthe area where a tab was to be formed (the area where a tab was to beformed should not be coated with electrode material), cutting the anodehaving anodic material coated on both sides of an anode currentcollector to the size of 3.0 cm×4.4 cm of rectangle, except the areawhere a tab was to be formed (the area where a tab was to be formedshould not be coated with electrode material), cutting a multi-layeredpolymer film prepared in a manner mentioned above to the size of 3.1cm×4.5 cm, interposing the above film between the anode and the cathode,and passing it through a roll laminator of 100° C. to laminate theelectrodes and the separator layer.

[0070] (Stacking Full Cells)

[0071] After preparing the polymer film 19 for the polymer electrolytemanufactured as above by cutting longitudinally, the seven full cellswere disposed alternately on and below the separator film 19 as shown inFIG. 7a. FIG. 7b is a drawing showing the side of FIG. 7a The gapsbetween each cell were spaced equally but enough that the cells could bestacked and separated by the separator film in a Z-shape. The polarityof the tab was disposed as in FIGS. 7a and 7 b so that it coincided withthe polarities of the neighboring full cells. That is, the direction ofthe electrodes of the first full cells placed on and below the separatorfilm 19 was disposed in the sequence of cathode and then the anode, andthe direction of the electrodes of the second full cell and next fullcells was disposed alternately below and on the separator film in thereverse order.

[0072] The polymer film 19 having the full cells placed thereon waspassed through a roll laminator so that the full cells were bonded onand below the polymer film 19.

[0073] The bonded full cell 17 of the first spot was folded into aZ-shape. After the folding was finished, the remaining separator film 19wrapped the outer side of the stacked full cells once and was fixed andsecured tightly by a tape 27.

[0074] (Preparing a Battery)

[0075] The full cell stacked battery prepared as above was placed withinthe aluminum laminate package. Then the liquid electrolyte comprising1:2 weight ratio of EC/EMC of 1 M LiPF₆ was injected and packaged.

[0076] (Evaluation)

[0077] Using the charging and discharging experiment, the evaluation ofthe cycle characteristic of the battery is shown in FIG. 8. Referencenumeral 102 shows the cycle characteristic of the manufactured batterywhere 0.2 C is charged and 0.2 C is discharged.

Example 2

[0078] Preparing a Stacked Cell where a Full Cell is a Basic Unit

[0079] (Preparing a Cathode)

[0080] Each cathode was prepared in a manner identical to the example 1.

[0081] (Preparing an Anode)

[0082] Each anode was prepared in a manner identical to the example 1.

[0083] (Preparing a Separator Layer; a Separator Film; a Polymer Filmfor Polymer Electrolyte)

[0084] Each separator layer and polymer film for polymer electrolyte forseparator film was prepared in a manner identical to the example 1.

[0085] (Preparing a Full Cell)

[0086] The eight full cells 17 of FIG. 1 were prepared by passingthrough a roll laminator of 100° C. to laminate the electrodes and theseparator layer as in example 1.

[0087] (Stacking Full Cells)

[0088] After preparing the polymer film 19 for the polymer electrolytemanufactured as above by cutting longitudinally, the eight full cellswere disposed on or below the separator film 19 as shown in FIG. 9a.FIG. 9b is a drawing showing the side of FIG. 9a. The gaps between eachcell were spaced equally but enough that the cells could be stacked andseparated by the separator film in a Z-shape where the distance was theaddition of width and thickness of the full cell. The polarity of thetab was disposed as in FIGS. 9a and 9 b so that it coincided with thepolarities of the neighboring full cells. That is, the direction of theelectrodes of the first full cells placed on and below the separatorfilm 19 was disposed in the sequence of cathode and then the anodeidentically, and the direction of the electrodes of the second full celland next full cells was disposed below and on the separator film 19 inthe reverse order.

[0089] The polymer film 19 having the full cells placed thereon waspassed through a roll laminator so that the full cells were bonded onand below the polymer film 19.

[0090] The bonded full cell 17 of the first spot was folded into aZ-shape. After the folding was finished, the remaining separator film 19wrapped the outer side of the stacked full cells once and was fixed andsecured tightly by a tape 27.

[0091] (Preparing a Battery)

[0092] The full cell stacked battery prepared as above was placed withinthe aluminum laminate package. Then the liquid electrolyte comprising1:2 weight ratio of EC/EMC of 1 M LiPF₆ was injected and packaged.

[0093] (Evaluation)

[0094] Using the charging and discharging experiment, the evaluation ofthe cycle characteristic of the battery is shown in FIG. 8. Referencenumeral 103 shows the cycle characteristic of the manufactured batterywhere 0.2 C is charged and 0.2 C is discharged.

Example 3

[0095] Preparing a Stacked Cell where a Bicell is a Basic Unit

[0096] (Preparing a Cathode)

[0097] Each cathode was prepared according to the method same as theabove example 1.

[0098] A cathode of the bicell was prepared by coating the slurry onboth sides of aluminum foil. That is, the cathode has a cathodicmaterial coated on both sides of the aluminum cathode current collector.The thickness of the both-side coated cathode was 140 μm.

[0099] (Preparing an Anode)

[0100] Each anode was prepared according to the method same as the aboveexample 1.

[0101] An anode of the bicell was prepared by coating the slurry on bothsides of copper foil. That is, the anode has an anodic material coatedon both sides of the copper anode current collector. The thickness ofthe both-side coated anode was 135 μm.

[0102] (Preparing a Separator Layer; a Separator Film; a Polymer Filmfor Polymer Electrolyte)

[0103] The separator layers, separator films, and polymer film forpolymer electrolyte were prepared in a manner identical to the example1.

[0104] (Preparing a Bicell)

[0105] The cathode having aforesaid cathodic material coated on bothsides of the cathode current collector was cut to the size of 2.9 cm×4.3cm of rectangle, except for the area where a tab was to be formed. Theanode having anodic material coated on both sides of the anode currentcollector was cut to the size of 3.0 cm×4.4 cm of rectangle, except forthe area where a tab was to be formed.

[0106] Four bicells 23 of FIG. 4a were prepared by placing both-sidecoated anode in the middle and the both-side coated cathodes at bothouter sides, placing a multi-layered polymer film prepared according tothe aforesaid manner which was cut into the size of 3.1 cm×4.5 cmbetween each anode and each cathode, and passing it through a rolllaminator of 100° C. to thermofuse the electrodes and the separatorlayer. Other bicells, that is, three bicells 24 of FIG. 4 b wereprepared by placing the both-side coated cathode in the middle and theboth-side coated anodes at both outer sides, placing a multi-layeredpolymer film prepared according to the aforesaid manner which was cutinto the size of 3.1 cm×4.5 cm between each anode and each cathode, andpassing it through a roll laminator of 100° C. to laminate theelectrodes and the separator layer.

[0107] (Stacking Bicells)

[0108] After preparing the polymer film 19 for the polymer electrolytemanufactured as above by cutting longitudinally, four bicells 23 andthree bicells 24 prepared as above were placed on the separator film 19and below the film respectively. FIG. 10b is a drawing showing the sideof FIG. 10a. The gaps between each cell were spaced equally but enoughthat the cells could be stacked and separated by the separator film in aZ-shape. The polarity of the tab was disposed as in FIGS. 10a and 10 bso that it coincided with the polarities of the neighboring bicells.That is, the direction of the electrodes of the first bicell placed onthe separator film 19 was disposed in the sequence of cathode and thenthe anode, and the direction of the electrodes of the second bicell andnext bicells was disposed alternately below and on the separator film 19in the reverse order.

[0109] The polymer film 19 having the bicells placed thereon was passedthrough a roll laminator so that the bicells were bonded on and belowthe polymer film 19.

[0110] The bonded bicell 23 of the first spot was folded into a Z-shape.After the folding was finished, the remaining separator film 19 wrappedthe outer side of the stacked bicells once and was fixed and securedtightly by a tape 27.

[0111] (Preparing a Battery)

[0112] The stacked bicell battery prepared as above was placed withinthe aluminum laminate package. Then the liquid electrolyte comprising1:2 of EC/EMC of 1 M LiPF₆ was injected and packaged.

[0113] (Evaluation)

[0114] Using the charging and discharging experiment, the evaluation ofthe cycle characteristic of the battery is shown in FIG. 11. Referencenumeral 104 shows the cycle characteristic of the manufactured batterywhere 0.2 C is charged and discharged at first and second time followedby 0.5 C charges/1 C discharges from the third time from which it isillustrated on the graph.

Example 4

[0115] Preparing a Stacked Cell where a Bicell is a Basic Unit

[0116] (Preparing a Cathode)

[0117] Each cathode was prepared according to the method same as theabove example 1.

[0118] (Preparing an Anode)

[0119] Each anode was prepared according to the method same as the aboveexample 1.

[0120] (Preparing a Separator Layer; a Separator Film; a Polymer Filmfor Polymer Electrolyte)

[0121] The separator layers and separator film, that is, polymer filmfor polymer electrolyte were prepared in a manner identical to theexample 1.

[0122] (Preparing a Bicell)

[0123] Four bicells 23 and four bicells 24 were prepared as in example3.

[0124] (Stacking Bicells)

[0125] After preparing the polymer film 19 for the polymer electrolytemanufactured as above by cutting longitudinally, four bicells 23 andfour bicells 24 prepared as above were placed on the same location ofthe separator film 19 with the bicell 24 upper side and the bicell 24lower side so that the bicell 23 and the bicell 24 were placedalternately as shown in FIG. 12a. FIG. 12b is a drawing showing the sideof FIG. 12a. The gaps between each cell were spaced equally but enoughthat the cells could be stacked and separated by the separator film in aZ-shape where the distance was the addition of width and thickness ofthe bicell. The polarity of the tab was disposed as in FIGS. 12a and 12b so that it coincided with the polarities of the neighboring bicells.That is, the direction of the electrodes of the first bicells placed onand below the separator film 19 was disposed in the sequence of cathodeand then the anode identically, and the direction of the electrodes ofthe second bicell and next bicells was disposed below and on theseparator film 19 in the reverse order.

[0126] The polymer film 19 having the bicells placed thereon was passedthrough a roll laminator so that the biceps were bonded on and below thepolymer film 19.

[0127] The bonded bicell 17 of the first spot was folded into a Z-shape.After the folding was finished, the remaining separator film 19 wrappedthe outer side of the stacked bicells once and was fixed and securedtightly by a tape 27.

[0128] (Preparing a Battery)

[0129] The stacked bicell battery prepared as above was placed withinthe aluminum laminate package. Then the liquid electrolyte comprising1:2 of EC/EMC of 1 M LiPF₆ was injected and packaged.

[0130] (Evaluation)

[0131] Using the charging and discharging experiment, the evaluation ofthe cycle characteristic of the battery is shown in FIG. 11. Referencenumeral 105 shows the cycle characteristic of the manufactured batterywhere 0.2 C is charged and discharged at first and second time followedby 0.5 C charges/1 C discharges from the third time from which it isillustrated on the graph.

[0132] The electrochemical element according to the present inventionmultiply stacked with full cells or bicells as a unit cell is easy tomanufacture, has a structure which uses the space available efficiently,and can especially maximize the content of the active electrode materialso that a highly integrated battery can be implemented.

What is claimed is:
 1. An electrochemical element comprising electrochemical cells which are multiply stacked, said electrochemical cells formed by stacking full cells having a cathode, a separator layer, and an anode sequentially as a basic unit, and a separator film interposed between each stacked full cell wherein, said separator film has a unit length which is determined to wrap the electrochemical cells, and folds outward every unit length to fold each electrochemical cell in a Z-shape starting from the electrochemical cell of a first spot to the electrochemical cell of the last spot continuously while the remaining separator film wraps an outer portion of the stacked cell.
 2. The electrochemical element according to claim 1, wherein an outermost end of said separator film is fixed by taping.
 3. The electrochemical element according to claim 1, wherein an outermost end of said separator film is fixed by heat-sealing.
 4. The electrochemical element according to claim 1, wherein said separator film is selected from a group consisting of a micro-porous polyethylene film, a micro-porous polypropylene film, or a multi-layer film prepared by a combination thereof, and a polymer film for polymer electrolyte of polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymer.
 5. The electrochemical element according to claim 4, wherein said polymer film for polymer electrolyte comprises a primary micro-porous polymer layer and a secondary gelling polymer layer of polyvinylidene fluoride-chlorotrifluoroethylene copolymer.
 6. The electrochemical element according to claim 1, wherein said each cathode of the full cell is an electrode coated with a cathodic material on both sides of a cathode current collector, and said each anode is an electrode coated with an anodic material on both sides of an anode current collector.
 7. The electrochemical element according to claim 1, wherein each full cell placed in the outermost side of said electrochemical cell comprises a cathode coated with a cathodic material on a single side of a cathode current, or an anode coated with an anodic material on a single side of an anode current collector, and a current collector foil is placed in the outermost side.
 8. A method of manufacturing an electrochemical element comprising electrochemical cells which are multiply stacked and filled within a battery case, said electrochemical cells formed by stacking full cells having a cathode, a separator layer, and an anode sequentially as a basic unit, and a separator film having a unit length which is determined to wrap the electrochemical cells and folding outward every unit length to fold each electrochemical cell in a Z-shape starting from the electrochemical cell of a first spot to the electrochemical cell of the last spot continuously while the remaining separator film wraps an outer portion of the stacked cell, said separator film interposed between each stacked full cell comprising the steps of, a) placing a full cell on and below the separator film continuously or alternately; b) laminating said placed full cells and said separator film of a); and c) folding outward said laminated full cells and said separator film of b) to the full cell adjacent next to the first full cell to fold each full cell in a Z-shape and wrapping the remaining separator film round an outer portion of the stacked full cell at least once so that each full cell is stacked.
 9. The method according to claim 8, further comprising a step of d) fixing the end of said separator film by taping.
 10. The method according to claim 8, further comprising a step of e) fixing the end of said separator film by heat sealing which carry out bring a thermo-welding machine, or a hot plate into contact with the separator film.
 11. The method according to claim 8, wherein said each full cell of a) is placed on or below the separator film.
 12. An electrochemical element comprising electrochemical cells which are multiply stacked, said electrochemical cells formed by stacking i) a bicell having a cathode; a separator layer; an anode; another separator layer; and another cathode sequentially as a basic unit; or ii) a bicell having an anode; a separator layer; a cathode; another separator layer; and another anode sequentially as a basic unit; and a separator film interposed between each stacked bicells wherein, said separator film has a unit length which is determined to wrap the electrochemical cells, and folds outward every unit length to fold each electrochemical cell in a Z-shape starting from the electrochemical cell of a first spot to the electrochemical cell of the last spot continuously while the remaining separator film wraps an outer portion of the stacked cell.
 13. The electrochemical element according to claim 12, wherein an outermost end of said separator film is fixed by taping.
 14. The electrochemical element according to claim 12, wherein an outermost end of said separator film is fixed by heal-sealing.
 15. The electrochemical element according to claim 12, wherein said separator film is selected from a group consisting of a micro-porous polyethylene film, a micro-porous polypropylene film, or a multi-layer film prepared by a combination thereof, and a polymer film for polymer electrolyte of polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymer.
 16. The electrochemical element according to claim 15, wherein said polymer film for polymer electrolyte comprises a primary micro-porous polymer layer and a secondary gelling polymer layer of polyvinylidene fluoride-chlorotrifluoroethylene copolymer.
 17. The electrochemical element according to claim 12, wherein said electrochemical cells are formed by alternately stacking i) a bicell having a cathode; a separator layer; an anode; another separator layer; and another cathode sequentially; and ii) a bicell having an anode; a separator layer; a cathode; another separator layer; and another anode sequentially.
 18. The electrochemical element according to claim 12, wherein said each cathode of the bicell is an electrode coated with a cathodic material on both sides of a cathode current collector, and said each anode is an electrode coated with an anodic material on both sides of an anode current collector.
 19. The electrochemical element according to claim 12, wherein each bicell placed in the outermost side of said electrochemical cell comprises a cathode coated with a cathodic material on a single side of a cathode current collector, or an anode coated with an anodic material on a single side of an anode current collector, and a current collector foil is placed in the outermost side.
 20. A method of manufacturing an electrochemical element comprising electrochemical cells which are multiply stacked, said electrochemical cells formed by alternately stacking i) a bicell having a cathode; a separator layer; an anode; another separator layer; and another cathode sequentially as a basic unit; or ii) a bicell having an anode; a separator layer; a cathode; another separator layer; and another anode sequentially as a basic unit; and a separator film having a unit length which is determined to wrap the electrochemical cells and folding outward every unit length to fold each electrochemical cell in a Z-shape starting from the electrochemical cell of a first spot to the electrochemical cell of the last spot continuously while the remaining separator film wraps an outer portion of the stacked cell, said separator film interposed between each stacked bicell comprising the steps of, a) placing a bicell on and below the separator film continuously or alternately; b) laminating said placed bicells and said separator film of a); and c) folding outward said laminated bicells and said separator film of b) to the bicell adjacent next to the first bicell to fold each bicell in a Z-shape and wrapping the remaining separator film round an outer portion of the stacked bicell at least once so that each bicell is stacked.
 21. The method according to claim 20, further comprising a step of d) fixing the end of said separator film by taping.
 22. The method according to claim 20, further comprising a step of e) fixing the end of said separator film by heat sealing which carry out bring a thermo-welding machine, or a hot plate into contact with the separator film.
 23. The method according to claim 20, wherein said each bicell of a) is placed on or below the separator film.
 24. The method according to claim 20, wherein said electrochemical cells are formed by alternately stacking i) a bicell having a cathode; a separator layer; an anode; another separator layer; and another cathode sequentially; and ii) a bicell having an anode; a separator layer; a cathode; another separator layer; and another anode sequentially. 